This invention relates to a composition for mixing with an oil and water mixture to allow it to be filtered through a pressure filter press to remove solids and specifically relates to the dewatering of petroleum oil sludges. The invention will be described in detail in its specific relation to a process for treating oil sludges with hydrated lime and calcined perlite so that the treated sludge can be passed through a diatomateous earth coated filter press and the filtered oil and water thereafter separated by gravity. The solids are removed in the filter cake which is non-leaching and meets environmental protection standards for disposal in non-hazardous waste disposal areas.
The composition of this invention comprises a filter aid of hydrated lime and calcined perlite of a specific size distribution.
Presently, dewatering of petroleum oil sludges is a major problem in places such as refineries, oil production fields, barge and tanker lines, oil pipeline and oil marketing terminals.
In the production of oil from an oil well, the oil often will flow to the surface from natural pressure during the first portion of the life of the well. However, after a certain period of pumping oil from the well, water must be forced into the formation to keep oil flowing from the well. A mixture of oil and water then is pumped from the well and this goes to a series of tanks and settling basins where as much of the oil as possible is removed for processing. Some of the oil and water is not separated and remains in the settling basin as sludge.
When the well is abandoned, the settling basins also are abandoned. There is a certain amount of usable oil in these basins which it would be desirable to recover for processing as the price of crude increases. Also government is continually increasing the strictness of pollution laws and certain states require elimination of a fixed percentage of the settling basins each year. To eliminate these, a method of separating the oil from the sludge must be utilized or the entire mass must be disposed of in some manner. With tighter controls on solid waste disposal, suitable dump sites are limited.
Even when the oil is separated from the sludge, disposal problems for the solids exist, because the solids must be a non-leaching mass so that pollution of the soil and ground water in later years is avoided. These problems exist in other areas such as refineries and terminals for oil and oil products.
Presently, several methods of treating oily sludges are used, but all have certain drawbacks and difficulties inherent in their use. It is conventional in the art to mix sludge and certain chemicals in a tank and pass the treated sludge through a pre-coated filter press.
One of the chemicals used to treat the sludge is 20-100% lime (based on the dry solids of the slduge) in the form of a milk of lime solution. With this treatment, some sludges can be properly conditioned and then dewatered with a pressure filter. However, when massive doses of lime are required, the net amount of sludge dewatered is reduced, thereby making the process uneconomical.
Another method presently used is to condition the raw sludge with 2.5-10% ferric chloride prior to adding lime in an amount of 10-40% by weight of dry sludge solids. Typically, this is approximately 400 mg ferric chloride per liter of sludge coupled with the milk of lime addition needed to adjust pH from between 8 to 11. Ferric chloride is used to reduce the amount of lime required. The ferric chloride forms a floc which is unstable on the acid side. Lime stabilizes the floc and adds filter cake body. Sludge conditioned in this matter can be processed by pressure filtration. This process is particularly useful where biological solids are present and oil concentrations are low. However, the ferric chloride is expensive and the process is not suitable in many sludge conditions.
Use of a heat treatment step in combination with the addition of polymers or lime also is used. When the additive is a polymer, the polymer is added to the sludge in a conditioning tank prior to 24-hour heat treatment of the sludge to effect a solids settling. After settling has occurred, oil is decanted and reclaimed off the top of the conditioning tank. The settled sludge solids are disposed of by various methods.
When heat treatment is combined with a lime addition, the amount of lime required is reduced. The sludge is heat treated, often in conjunction with pH adjustment, prior to the addition of lime. The amount of lime added after heat treatment ranges from 10-40% by weight of dry sludge solids and is introduced in a milk of lime solution. Heat treatment alters the flow characteristics of the sludge affecting a more efficient oil/water from solids separation under pressure filtration.
In either of the processes using heat treatment, the amount of energy required is excessive and makes the process uneconomical.
A final process used to clean up a sludge is to add conventional body feeds or bulking agents, such as diatomaceous earth and fly ash, to increase porosity and add filter cake body under pressure filtration.
These processes have the disadvantage that massive doses are required (as much as 1 pound per gallon of sludge). This makes the process uneconomical. Another disadvantage is that diatomaceous earth and fly ash will often coat and blind with oil.
One of the principal objects of this invention is to provide a filter aid for use with pressure filters in treating oil and water mixtures wherein the solids are separated from the oil and water which then can be separated by decantation. The filter aid is a combination of lime and calcined perlite of specific size distribution.
Another principal object of this invention is to provide a universal method of conditioning oily sludge prior to pressure filtration, thereby effecting an economical method of recovering oil and producing a non-leaching well consolidated filter cake which can be disposed of safely.
Still another object is to provide a method of treating sludge concurrently or sequentially with lime and calcined perlite of a defined size distribution whereby the treated sludge, when passed through a pressure filter, will have the solids separated from the oil and water, and the oil can be separated by decantation from the recovered filtrate.
These and other objects and advantages will become apparent hereinafter.